The invention relates a method and apparatus for inhibiting or eliminating the development of colonization by microorganisms on tissue and indwelling medical devices and the subsequent occurrence of infections associated with same.
1. Field of the Invention
Infections associated with medical care are a major cause of morbidity and mortality. These infections are typically very costly to manage and may be associated with a variety of adverse outcomes including death. Common types of infections that develop in an acute care setting include pneumonia, urinary tract infection, wound infection and blood stream infection. Often these infections develop from the use of invasive devices in patients with limited resistance to infection as a result of their underlying illnesses or drug therapy.
Also, because many strains of microorganisms acquired in the hospital are resistant to commonly used antibiotics, it is often difficult and costly to treat these infections.
Medical catheter or device-related infections such as those associated with urinary, intravenous, intraarterial, dialysis and other types of medical catheters or other implanted medical devices usually result because of a breech of natural protective mechanisms present at sites such as the skin or the urethra. In these situations, the development of infection is believed to involve the following steps:
1. Microorganisms colonize and multiply on the patient""s skin. There is a microbial flora normally present on the skin. However, when a patient is admitted to a health care setting, organisms from this environment (typically resistant to antimicrobials) become part of the patient""s flora soon after admission;
2. After insertion of a catheter or other medical device, these organisms continue to multiply and begin to colonize the surface of the catheter or device;
3. As the organisms continue to multiply, they spread on the external and/or internal surface of the catheter or device and eventually into normally sterile tissues (e.g. blood vessels, abdomen, bladder, etc.). This process is facilitated by development of a biofilm (which consists of proteins from the blood or tissue fluid and other debris) on the surfaces of the devices;
4. Once in these normally sterile sites, the organisms continue to multiply and development of a clinical infection may result.
It has been known for many years that Staphylococcus aureus, for example, nearly always can be found to colonize the patients that develop infection with this organism, colonization meaning the presence of organism without evidence of infection.
The most important site for colonization is the anterior part of the nose (anterior nares). Individuals that develop a staphylococcal infection at the site of a wound, an indwelling catheter or prosthetic device usually has nasal colonization with this organism.
2. Description of the Prior Art
A variety of techniques have been used in an attempt to reduce the frequency of those infections. These have included impregnating catheters and devices with antibiotics, incorporating silver or silver compounds in the catheters and making the catheters or devices of different materials, e.g. silastic, and applying an electric current to the catheter. Each of these prior methods has, to some extent, reduced the frequency of infection. However none of these prior techniques is ideal. An ongoing concern is that microorganisms have the potential to develop resistance to the antimicrobials incorporated into the catheter or device in an attempt to prevent infection.
It is also known that various portions of the electromagnetic spectrum that include light are known to effectively kill microorganisms. Thus, white light radiation has been used in the treatment of nose and throat passages and ultraviolet light has been used to kill airborne bacteria, especially on tuberculosis wards. Although not extensively studied, light of other wavelengths is also capable of killing microorganisms.
Photodynamic therapy is the use of light with certain chemicals that are activated by the light energy. The chemicals that are used (referred to as photosensitizers) may be naturally occurring compounds (e.g. porphyrins, polyynes, psoralens and anthraquinones), dyes (e.g. methylene blue, Bengal Rose, toluidine blue, rhodamines, etc.) or other unrelated agents (e.g. cyanine compounds), that have antimicrobial activity alone or on exposure to light.
Light energy, which for purposes of this application means that part of the spectrum between 200 nm and 1400 nm which includes ultraviolet, visible and infrared light, acts on these chemical substances in different ways to result in an antimicrobial effect. Most often, the effect is to liberate an activated oxygen molecule (so-called singlet oxygen) which is able to destroy both cells and tissues. For each photosensitizer, there is a corresponding wavelength of light that causes optimal activation. For example, toluidine blue is optimally activated at a wavelength of about 626 nm. The wavelength at which there is a maximum effect may be modified by manipulating the photosensitizer molecule; alkyl substitution of the amino groups and halogenation of the chromagen both increase the wavelength associated with maximum activity.
The light energy may be laser generated or from another source such as an incandescent, fluorescent or halogen bulb or a light emitting diode. It may be of narrow spectrum or may include differing wavelengths and it may be pulsed or constant. With light in the ultraviolet part of the spectrum, it is known that pulsed light allows bacterial killing at energy levels orders of magnitude less than required with constant light.
Photosensitizers have differing degrees of activity against both bacteria and tissues. Some are more selectively active against microorganisms and are less toxic to tissues. Other photosensitizers are quite toxic to tissues. Photosensitizers that are tissue toxic have been used with light administration in the treatment of a variety of tumors. Although most of the recognized photosensitizers are antimicrobial, the mechanism of action varies somewhat. For example, methylene blue causes fatal changes in the nucleic acid in Proteus.
Chemical modification of the photosensitizers (e.g. differing side chains, molecular size, etc.) significantly impacts their activity. For example, among the furanocoumarin photosensitizers, replacement of an oxygen with sulfur or selenium is associated with markedly increased photoactivity. Dimethyl-methylene blue is substantially more active than methylene blue against most bacteria. Also, the lethal effect may be modified by the presence of various inorganic salts.
In addition to the activity of light on bacteria and other microorganisms (alone or with a photosensitizer), light energy may also have other effects that are beneficial in preventing or limiting infection. For example, ultraviolet light is able to markedly reduce the adhesion of bacteria to surfaces and to limit the development of biofilms. In addition, exposure to light may limit production of toxic bacterial substances, such as super antigens produced by Gram-positive bacteria.
Despite the fact that photodynamic therapy has been known for many years, we know of no implementations of that therapy that are effective to inhibit colonization of tissues with microorganisms and prevent infections associated with implanted medical catheters and devices.
Accordingly, it is an object of the invention to inhibit or eliminate the colonization of tissues with harmful microorganism.
Another object of the present invention to provide an improved method to prevent infection associated with in-dwelling medical catheters and devices.
Still another object of the invention is to provide an improved medical catheter or device which prevents infections commonly associated with the implantation of same.
A further object of the invention is to provide such a medical catheter or device which has an inherent antimicrobial activity that prevents the colonization by bacteria on the surfaces of the in-dwelling catheter or device and tissue adjacent thereto.
Yet another object of the invention is to provide a medical catheter or device of this type whose antimicrobial activity may be tailored to the particular microorganisms likely to be present at its dwelling site.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying the features of construction, combination of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
Briefly in accordance with my invention, light energy together with a photosensitizer or photosensitizers is used to prevent the development of infection at the site of an in-dwelling medical catheter or device. More particularly, light of a selected wavelength or wavelength band is coupled to a catheter or device and transmitted by a wall or walls thereof or to either or both external and internal surfaces thereof. The wavelength of the light is selected so that when the catheter or device is indwelling in a patient, the light illuminating the surface(s) and tissue has a toxic effect on microorganisms that tend to build up on the surface(s) at the implantation site. The catheter or device itself also incorporates a photo sensitizer(s) which releases a toxic substance at the surface(s) which is activated by the light energy thereby increasing the antimicrobial activity of the catheter or device.
For purposes of this application, a xe2x80x9ccatheterxe2x80x9d means any cannula with one or more lumens used to 1) deliver fluid and drugs to the vascular system or other tissues (e.g. the cerebrospinal fluid), 2) access the vascular system for various reasons (e.g. pressure monitoring, hemodialysis) or 3) irrigate or drain body tissue. Examples of such tissues include bladder, abdomen, chest cavity, intracranial or intrathecal cavities, wounds, joints, etc. The word xe2x80x9cdevicexe2x80x9d refers to types of medical equipment other than catheters that are normally inserted into sterile tissues, examples being nose and throat applications, stents, cardiac pacing leads and the like.